Rotational state-changing cold collisions of hydroxyl ions with helium

TL;DR

This paper introduces a method to measure quantum state-to-state collision rates of hydroxyl ions with helium at low temperatures, revealing detailed insights into cold molecular collisions and quantum resonances.

Contribution

It provides the first absolute quantum scattering rate coefficients with full quantum state control for hydroxyl anions colliding with helium, validated by experiment and theory.

Findings

Excellent agreement between experiment and quantum scattering theory.

Similar rate coefficients for different isotopes due to quantum resonances.

Method applicable to polyatomic systems and non-radiative processes.

Abstract

Cold molecules are important for many applications, from fundamental precision measurements, quantum information processing, quantum-controlled chemistry, to understanding the cold interstellar medium. Molecular ions are known to be cooled efficiently in sympathetic collisions with cold atoms or ions. However, little knowledge is available on the elementary cooling steps, because the determination of quantum state-to-state collision rates at low temperature is prohibitively challenging for both experiment and theory. Here we present a method to manipulate molecular quantum states by non-resonant photodetachment. Based on this we provide absolute quantum scattering rate coefficients under full quantum state control for the rotationally inelastic collision of hydroxyl anions with helium. Experiment and quantum scattering theory show excellent agreement without adjustable parameters. Very similar rate coefficients are obtained for two different isotopes, which is linked to several quantum scattering resonances appearing at different energies. The presented method is also applicable to polyatomic systems and will help shed light on non-radiative processes in polyaromatic hydrocarbons and protein chromophores.